The present invention broadly relates to a rubber composition. More specifically, the invention relates to such a rubber composition which has performance characteristics suitable for use of the rubber composition for tire treads.
Rubber-reinforcing carbon blacks are classified into a wide variety of kinds, depending on properties which they have, and the particular characteristics of respective kinds of carbon black constitute an important factor determinative of the performance characteristics of rubber compositions in which the carbon blacks are blended.
Thus, in blending a carbon black in a rubber component, it is widely practiced to make a selective use of a carbon black of suitable characteristics for the intended utility of the rubber composition.
For example, for the use of a rubber composition as a rubber member, such as a tire tread for example, which is required to possess a high abrasion resistance under severe service conditions, it is generally accepted to be effective to use such a carbon black which has a relatively small particle diameter and a relatively large specific surface area like, for example, SAF (super abrasion furnace), ISAF (intermediate super abrasion furnace) and HAF (high abrasion furnace) carbon blacks.
However, in the preparation of a rubber composition, to use a carbon black belonging to hard type ones such as the above ones tends to accompany not only an adverse affect on the ease of dispersion and the processability in the blending preparation of the rubber composition but also a disadvantageous increase of the heat generating propensity of the resulting rubber composition.
A lowering of the ease of dispersion and the processability means such a phenomenon in which, during the process of kneading a carbon black with a rubber component, the hardness of the blending components under kneading becomes so considerably increased that it becomes disturbed to smoothly operate a homogeneous dispersion. This phenomenon forms a factor of not only an increase in the required energy and time for the kneading operation but also a degradation of the quality and the performance characteristics of the product rubber composition.
Then, an increase in the heat generating propensity of the rubber composition is causative of a heat build-up which takes place in a tire due to a hysteresis loss during running of the tire and which gives rise to a danger such as a destruction of the tire interior structure or an aging of the tire forming material.